The present invention relates broadly to the soilless cultivation of plants and more particularly relates to an improved apparatus and method for the aeroponic cultivation of plants.
Hydroponic growth apparatus, either for decorative purposes in a home or for commercial purposes such as in a greenhouse, are known. Typical of various U.S. patents disclosing such apparatuses are: U.S. Pat. No. 4,033,072, to Kobayashi et al.. dated Jul. 5, 1977; U.S. Pat. No. 4,218,847, to Leroux, dated Aug. 26, 1980; U.S. Pat. No. 4,454,684, to O'Hare, dated Jun. 19, 1984; U.S. Pat. No. 4,756,120, to Arledge, dated Jul. 12, 1988; U.S. Pat. No. 4,951,416, to Gutridge, dated Aug. 28, 1990; and U.S. Pat. No. 4,986,027, to Harvey, dated Jan. 22, 1991. In general, according to the article "Hydroponics: Soilless Gardening", appearing in Volume 5 of New Illustrated Encyclopedia of Gardening, The Greystone Press, New York, N.Y., 1960, "hydroponic" plant culture can be broadly defined as the cultivation of plants in a soilless media wherein substantially the entirety of nutrients supplied to the plant roots is accomplished by wetting of the plant roots with an appropriate aerated nutrient solution containing, as solutes, the necessary plant nutrients. Thus, the plant roots in hydroponic plant cultures can be supplied by a pool of nutrient solution in which the plant roots are directly immersed or by wetting of a porous inert aggregate material such as sand, gravel, vermiculite, expanded mica, crushed stone, cinders, bricks, glass beads, ground lava and the like and within which aggregate material the plant roots reside. The nutrient solutions utilized in the hydroponic cultivation of plants usually contain solutes comprising not only the primary plant growth elements of nitrogen, potassium and phophorous, but also the micronutrient or trace elements essential to the healthy growth of the particular plant species involved, such as calcium, magnesium, boron, iron, manganese and the like. Additionally, the nutrient solution is often aerated such that the solution applied to the plant roots contains adequate dissolved oxygen to sustain plant growth. Moreover, the p.sup.H of the nutrient solution is normally controlled to within the optimum range for the particular plant species involved. In respect of hydroponic pool systems, one of the methods commonly employed is generally termed as the "flood and drain" method. Here, a horizontally disposed tray containing the roots of the growing plants is cyclically flooded with a nutrient solution. Upon completion of the flood cycle the tray is drained into a recycle receptacle for subsequent recycle of the nutrient solution at the next flood cycle. The drain cycle is an important element of the system since the plant roots, if allowed to remain continuously immersed in the nutrient solution, would be subject to the danger of suffocation. Such "flood and drain" hydroponic systems, due to the physics and geometry of bulk water flow, inherently require that the plants be arranged in a planar array relative to the tray, thereby limiting the number of plants which can be grown per unit surface area thereof.
It has been found that hydroponic plant culture often results in faster plant growth and maturation and greater flower or fruit yields relative to conventional field and greenhouse soil culture methodologies. It is generally theorized that these benefits flow from the fact that, as compared to conventional soil culture methodolgies, the plant roots in hydroponic culturing are substantially relieved of the energy-consuming burden of searching and growing through nutrient-poor soils in order to obtain adequate plant nutrition. Thus, in hydroponic plant cultivation, the plant energy normally devoted to root growth is, instead, at least partially made available to the growth and maturation of the plant, thereby resulting in earlier maturation and more prolific flower or fruit yield. In support of this theory it is often found that the root systems of mature flowering or fruiting plants grown hydroponically are substantially shorter or of lesser overall mass than those of similar plants grown in conventional soils.
"Aeroponic" plant culture refers to a sub-genus of hydroponics in which neither a root supportive particulate media nor a root immersion pool of nutrient solution is employed. Instead, in aeroponic plant culture, the plants are generally supported in a vertically oriented elongate chamber whose side wall is perforated with a plurality of plant site apertures to receive the plants and within which chamber the plural plant roots reside suspended, in free space. The foliage of the plants is, of course, stationed exterior of the chamber, thereby to receive light. A nutrient solution is sprayed cyclically or continuously from the top of the chamber, upon the bare plant roots contained therewithin. As in the flood and drain hydroponics system, excess nutrient spray solution may be collected from the bottom of the chamber, any particulate matter filtered and/or settled out therefrom, and recycled to the spray nozzles. Aeroponic plant culture provides a number of advantages over other hydroponic systems. Firstly, no aggregate material is utilized, thereby providing obvious expense, weight, handling and clean-up advantages. Secondly, because the plant roots remain bare, individual plants in an aerooponics system can usually be readily removed with their root systems intact. This becomes a particularly important feature in transplantation or where plant disease or infestation occurs and wherein removal of the entirety of the diseased or pest ridden plants from the system, without residue, is highly desirable. Too, aeroponic cultivation permits arrangement of the growing plants circumferentially and vertically about the root chamber, thereby permitting closer packing of the plant stock and more efficient use of nursery space than is afforded by the aforementioned flood and drain hydroponics system.
In accordance with the present invention, it has now been found that the plant growth and maturation rate advantages generally associated with the hydroponic cultivation of plants over other forms of plant culture can be even further improved in aeroponic systems when atmospheric air is affirmatively inducted into the root chamber of the aeroponic plant growing apparatus and stale air is exhausted therefrom, at least during the period of spraying of the plant roots with nutrient solution.
Beyond the foregoing, however, additional limitations and detriments relating to prior art aeroponic cultivation apparatuses and techniques have also been addressed and resolved in at least certain preferred embodiments of the invention. For instance, in known aeroponic systems, little or no provision is made for the facile removal, replacement and changing of sub-populations of plants whose root systems may have fallen prey to fungal, bacterial, viral or pest infestations or which plants may otherwise have been rendered of lesser quality of growth and maturation than other plants in the system. In accordance with the invention, however, an aeroponic growth system and method is provided wherein plural plants residing within said system may be quickly and conveniently removed, replaced and/or augmented.